Hydrogen peroxide bleaching under conditions in which concentrations of H.sub.2 O.sub.2 and alkali are low is a considerable challenge to the laundry detergent industry. Similar challenges are also faced by the formulator of automatic dishwashing detergent compositions (ADD's), which are expected to efficiently cleanse and sanitize dishware, often under heavy soil loads, typically involving mildly acidic food residues. The problems associated with the formulation of truly effective cleaning and bleaching systems have been exacerbated by legislation which limits the use of effective ingredients such as phosphate builders in many regions of the world.
Domestic bleaching systems for fabrics and hard surfaces can be simple, such as alkaline hypochlorite, but such systems are frequently potentially aggressive. More complex systems have evolved, centering on the use of a hydrogen peroxide source. Such systems can further involve mixtures of various detersive surfactants to remove a wide variety of soils and stains from surfaces. In addition, various detersive enzymes, soil suspending agents, non-phosphorus builders, optical brighteners, and the like may be added to boost overall cleaning performance. Many fully-formulated cleaning compositions having a bleaching action contain oxygen bleach, which can be a perborate or percarbonate compound. While quite effective at high temperatures, perborates and percarbonates lose much of their bleaching function at the low to moderate temperatures increasingly favored in consumer product use. Accordingly, various bleach activators such as tetraacetylethylenediamine (TAED) and nonanoyloxy-benzenesulfonate (NOBS) have been developed to potentiate the bleaching action of perborate and percarbonate across a wide temperature range. NOBS is particularly effective on "dingy" fabrics.
A limitation with activators such as the widely commercialized TAED is that the wash solution or liquor should have a pH of about 10 or higher for best results. Since soils, especially from foods, are often acidic, detergent products are frequently quite alkaline or are buffered sufficiently to maintain a high pH so the bleach activator system can operate effectively throughout the wash. However, this need runs counter to providing milder formulations which could be improved in their compatibility with fabrics, glassware and/or skin. In cleaning operations below pH 10, many of the existing bleach activators lose their effectiveness or undergo competing side reactions which produce ineffective byproducts.
The search, therefore, continues for more effective activator materials, especially for use in mildly alkaline washing liquors or with decreased levels of perborate or other sources of hydrogen peroxide. Improved activator materials should be safe, effective, and will preferably be designed to interact with troublesome soils and stains. Various activators have been described in the literature. Many are esoteric and expensive.
It has now been determined that certain selected bleach activators are unexpectedly effective in removing soils and stains from fabrics and hard surfaces such as dishes even under low alkaline wash conditions or with decreased levels of hydrogen peroxide. These activators also have advantageously high ratios of rates of perhydrolysis to hydrolysis and of perhydrolysis to diacylperoxide formation. Without being limited by theory, these unusual rate ratios lead to a number of significant benefits for the instant activators, including increased efficiency, avoidance of wasteful byproduct formation in the wash, increased color compatibility, increased enzyme compatibility, and better stability on storage.
When selected and used as described herein, bleaching solutions are provided using the selected bleach activators to remove soils and stains not only from fabrics, but also from dishware in automatic dishwashing compositions, from kitchen and bathroom hard surfaces, and the like, with excellent results. The bleaching solutions are designed to function well over a wide range of washing or soaking temperatures and are compatible with rubber surfaces, such as those of sump hoses often used in European front-loading washing machines. Moreover, novel methods for producing such bleaching solutions are provided. In short, the compositions and methods herein provide a substantial advance over those known in the art, as will be seen from the disclosures hereinafter.